The invention concerns a vibration damper for the damping of fluid vibrations in a hydraulic system, especially in a hydraulic control circuit for a motor vehicle transmission wherein said vibration damper possesses an elastic, deformable damping element.
Vibration dampers of the above kind are installed in motor vehicle transmissions for the adjustment of the control pressure in the valves as well as for the damping of vibratory oscillations in the fluid pressure medium. The damping elements are customarily made of an elastomer and thus are elastically deformable upon changes in load from different fluid pressures.
DE 195 24 921 A1, for instance, discloses such a vibration damper. This patent teaches of a vibration damper with a membrane, which is constructed from an elastomer as a component in the form of a hollow cylinder. The failure of an elastomer membrane of this nature, for instance by leakage because of bursting, leads, generally, to the failure of the entire vibration damper. Because of this, the controlling pressure in the hydraulic system drops and the transmission is no longer controllable. This leads to contingent damage to the transmission and can finally result in the immobilization of the vehicle.
Thus, the purpose of the invention is to prevent a pressure loss at a vibration damper upon failure of the damping element, so that a transmission failure with contingent immobilization of the vehicle is avoided.
This purpose is achieved, by a generic vibration damper, wherein a sealing element is provided, which secures the function of the hydraulic system upon a failure of the damping element, for instance by leakage because of bursting. In this way, advantageously, a free fluid through-flow action is blocked, so that upon a failure of the damping element a pressure drop in the hydraulic control circuit is prevented. Even in the case of a defective damping element, the function of the transmission remains essentially in force and an immobilization of the vehicle is avoided. If a possible difficulty in shifting quality appears, which can occur from a burst damping element, then as a matter of course, the damping element is to be replaced.
A preferred embodiment of the invention offers the proposition, that the damping element be placed in a recess of a housing, further, that this housing possess an opening, in particular, an orifice to serve as the inlet of a pressurized fluid to the damping element. In addition, a pressure equalization port in said housing is provided. With this arrangement, advantageously, the sealing element, in case of failure of the elastically deformable damping element, closes the pressure compensation opening. Thus, a solution is brought about, by which, during normal operation of the vibration damper, when the damping element exhibits no leakage, the vibrations of the fluid pressure are damped by elastic deformation and the pressure compensation opening is held open, so that a pressure equalization in two chambers before and after the said sealing element takes place and that, by means of the extenuation of the damping element, volumes of air compressed in the forward chamber escape through the pressure equalizing opening. As this happens, the chambers are defined before and after the sealing element, regarded in the direction of the flow from the throttle valve to the pressure equalizing opening.
In a further development, the proposal is made that the sealing element and/or the damping element be movably placed in the recess. In this way, several advantageous possibilities arise in the formulation of the two essential elements of the vibration damper.
In one advantageous design of the invention, it is proposed, that the pressure side orifice and the pressure equalization port be respectively placed in essentially oppositely situated end locations of the recess and that the sealing element be provided near to the orifice and the damping element be placed near to the pressure equalization port.
A particularly advantageous design of the vibration damper is found, wherein the sealing element is constructed as essentially a cylindrical piston, and the recess in the housing is bored as a piston boring in which the said piston is guided to be axially displaceable. In this arrangement, the cylindrical outer shell of the piston sealingly contacts the cylindrical inner wall of the piston boring, so that the two fluid chambers, located forward and after the two ends of the piston, are separated, one from the other.
In another development of the invention, the piston, on at least one end, is provided with a conically shaped boring, which serves to center the damping element.
The damping element itself is constructed as a sphere, wherein the diameter of the sphere is less than the diameter of the piston or the piston boring. In this way, the sphere is advantageously centered within said conically shaped boring at one end of the piston.
The piston, as well as the housing which encloses it, is comprised of materials with essentially equal heat expansion coefficients, so that by any possible heating of the vibration damper, the sealing function between the piston and the piston boring is advantageously assured.
The piston is advantageously made of a plastic, especially Ryton(copyright) or a similar construction material. The housing can be fabricated of aluminum or equal material.
The damping element, on the other hand, is made of an elastomer, especially nitrile butadiene rubber (NBR) or a similar raw material, and possesses accordingly, an advantageous damping characteristic.
In a further embodiment of the invention, the proposal is to place the damping element close to the orifice and the sealing element close to the pressure equalization port of the recess. In this way, advantageously, an arrangement is undertaken opposite to that of the previously described design with an reversed positioning of the two elements.
It is advantageous, if the damping element is designed as an essentially hollow cylindrical and elastically deformable component, and provided with one essentially open and one essentially closed end piece for the acceptance of the fluid in the internal chamber of the damping element.
The sealing element is essentially shaped as a circular plate, an annular ring, a plate, a cone, as a cup, or is a similarly shaped component and is placed preferably on the outside of the closed end of the damping element.
By the construction of the sealing element in a conical or cup shaped form, the said element opens favorably in the direction of the open end of the damping element and thus toward the orifice, so that in a case of the bursting of the damper element, and an escape of the pressurized fluid out of the damper element, an effective sealing function is accomplished by the sealing element.
In an additional development, the sealing element exhibits on its outer radial rim, a lip seal running essentially around its circumference. During normal operation of the damping element, this lip seal lies nearly completely against the inner wall of the recess, thereby dividing the recess into chambers, one forward and one after the said lip seal, as seen in the direction of the flow.
In a further design of the sealing element, the lip seal is shaped elliptically, so that it forms, within the predominately cylindrical construction of the inner wall of the recess, escape penetrations of specifically designed opening between the lip seal and the said inner wall.
In yet another, embodiment of the sealing element, especially to be preferred, the sealing element is essentially annular in shape and the diameter of the lip seal is, when not installed, greater than that of the inside diameter of the essentially cylindrical recess. By this means, assurance is given, that the lip seal, when installed, will lay stressed against the said inner wall of the recess.
So that a pressure exchange of the two chambers of the recess, before and after the lip seal, can be brought about, this seal is provided with at least one through opening.
The said through opening is advantageously so designed and the elasticity of the lip seal is selected in such a manner, that in the case of failure, for instance by bursting of the damping element, by means of which failure, due to the unilateral force of the existing fluid pressure in the chamber forward of the lip seal, a circumferential seal is formed by the said lip seal against the inner wall of the recess which encompasses the damper.
In this way, a simple solution is proposed, which assures, that after the bursting of the damper element, the lip seal is reliably pressed against the inner wall of the recess, and thereby closes the pressure equalization port. The efficiency of the damping is indeed lost to a considerable degree, however, the control pressure in the vibration damper does not lead directly to loss of function by the transmission.
In a further preferred embodiment of the invention, the sealing element is designed as an elastic, essentially circular, annular plate and is connected coaxially with the damping element.
When this is done, the sealing element is shaped in such a way, that it does not directly touch the inner wall of the recess during the normal operation of the vibration damper, so that the chamber forward of the sealing element communicates with a chamber behind the sealing element. With this arrangement, under normal operational conditions, a pressure equalization is effected between the two chambers before and after the sealing element with the result that upon the expansion of the damping element, the volumes of air pressed out of the forward chamber advantageously escape through the said pressure equalization port to the after chamber.
The sealing element itself, as well as the connecting of the sealing element onto the damping element is carried out in such a manner, that the sealing element, in case of failure, closes off the pressure equalization port. This can be effected, for instance, since the centralized and essentially neck shaped connection piece between the damping element and the sealing element is so elongated by the fluid pressure on the one side of the sealing element, that the said sealing element is pressed against a sealing seat of the recess.
Advantageously, the sealing element is designed to be flexible, so that it is elastically deformed in its radial, outward area by the fluid pressure on one side and is thus pressed against an annular sealing seat of the recess, thus closing the pressure equalization port.
The sealing element as well as the damping element are constructed as separate components. Thus, the exchange of a single defective component as well as the separate fabrication of the two components in different constructive materials becomes simple to do, so that each component can be made as a sealing element or a damper element from the most appropriate materials.
However, as an alternative, the sealing element and the damping element can be made in one-piece construction, for instance, from an elastomer. Such a one-piece proposal offers an especially economical production of the sealing element and the damping element.